The 500 pound World War Two device was picked up during dredging work.
Christchurch Council Criticised For Sandbag Charges
David Cameron has insisted councils should not be charging residents in flood-hit areas for sandbags.
The Prime Minister said there was no need for town halls to recoup the costs because central government would cover them.
Christchurch Borough Council has been asking locals to pay £30 for a 'flood pack' of four standard sandbags and one to protect doorways.
A spokesman said: "The situation is that if an emergency is called then we will provide sandbags free of charge.
"We cannot provide them just because people are concerned about things... currently there are no alerts.''
Resident Steve Richards told the Bournemouth Echo: "My brother bought 50 at an incredibly high cost but 50 sandbags goes nowhere.
"We feel so helpless, pleading for help and no-one's giving it, yet you switch on the television and the Prime Minister is pledging that no-one will be left vulnerable and money's no object.''
Up until the end of last week, Tewkesbury Borough Council was issuing free bags to local people - but asking them to pay for sand to go in them.
A spokeswoman said it had now decided to be "flexible'' about the policy.
"In a situation like this we are issuing sandbags to anybody that needs them,'' she added.
Posting on Twitter, Mr Cameron said: "I've told local councils they should not charge for sandbags in flood-hit areas - central government will pick up the cost.''
Local government minister Brandon Lewis said: "There is absolutely no reason for any councils to be charging residents for sandbags.
"Councils are able to claim any costs for their emergency response to flooding back from Government under the Bellwin scheme.
"We have spoken to every local authority in the country and are confident that there are more than enough supplies to meet local needs, with volunteers and military support on the ground to make them ready.
"We are able to supply up to 10,000 sandbags a day, and councils such as Northamptonshire and Lincolnshire have been coming to the aid of neighbouring areas.''
Government sources said no council had reported any problems obtaining sandbags, and there were 25,000 filled and ready to be deployed.
They insisted local authorities would be able to claim back any cost through the Government's Bellwin Scheme, which provides assistance in emergencies.
Christchurch council said it had sold 29 "flood packs'' since Christmas.
The £30 price only covers the cost and there is no profit, a spokesman said.
The Local Government Association stressed that councils were not charging for sandbags in areas where a flooding alert was in force.
"Councils are not charging for sandbags for residents and businesses at risk of flooding. It is vital sandbags are distributed to areas where they are needed most and this is what local authorities have been doing,'' a spokesman said.
"Since the heavy rain and floods hit before Christmas, councils have worked around the clock to ensure residents are safe. They have cleared roads, opened emergency rest centres, rescued stranded motorists and distributed tens of thousands of sandbags.
"Councils are working closely with the emergency services and the Environment Agency to monitor the situation in their areas. When an emergency is declared, councils will act swiftly to ensure residents, homes and businesses are not affected, and will continue to work tirelessly to do so until the flood waters recede.
"The rain has been unprecedented and relentless but throughout the floods, and with more rain forecast, councils have been on the front line keep communities safe. This includes distributing sandbags for free.''
640 men were killed when the South African troop carrier was hit by a cargo ship in 1917.
The 79-year-old man suffered a serious head injury in the Cranmer Road car park in Winton.
Two Girls Indecently Assaulted Last Sunday
Recently Played Tracks
Now playing: Non-stop hit music
Deposit £10 to get a £40 Welcome Bonus - That's £50 to play bingo, slots and more!*
Over 50 tracks to make you feel-good. New album out now...
Find your local four day weather report here.
What's happening on the roads where you are?
Make Heart the soundtrack to your day and you could be a winner with great prizes up for grabs throughout the day.
Find out more about some of the companies advertising on Heart.
Get some great ideas on how to advertise your business on radio, online and on mobile.